Hulls with an off-shore work platform usually have a polygonal shape and from three to four vertical leg chords that are connected by truss work and that penetrate through the hull. Those chords can be lifted up or lowered relative to the hull.
As schematically shown in FIG. 2 in the accompanying drawing, the invention may be applied to a platform in which a longitudinal rack 3 is fixed on a vertical leg chord 2 that penetrates through the hull 1. On this hull the off-shore work platform is mounted. The rack 2 meshes with a plurality of pinions 5 mounted on a support frame 4 on the hull 1. When the pinions 5 are driven by a driving means 6 that is provided on the support frame 4, the leg chord 2 ascends or descends relative to the hull 1. After the bottom end of the leg chord touches the seabed, if the leg chord is further driven downward into the seabed, the hull 1 is raised off the surface of the sea 7 as shown in FIG. 2. Then the off-shore work platform can be raised to a desired from the surface of the sea 7 by driving the pinions 5 after the bottom end of the leg chord has been firmly embedded in the seabed.
One device to lock the off-shore work platform which has been positioned at a desired height is disclosed in U.S. Pat. No. 4,389,140. According to this patent, a wedge-shaped rack piece with a plurality of locking teeth is mounted on the hull in such a fashion that those locking teeth can either engage the rack on the leg chord or disengage it if desired. The locking teeth of the rack piece lock the hull by engaging the rack. The positioning of the engagement of the locking teeth with the rack can be adjusted by lifting up or lowering a guide block which has wedge faces. The guide block is moved by turning screw spindles which are mounted on the upper and lower sections of the rack piece.
Such conventional locking devices have some disadvantages. When an off-shore work platform is supported and fixed by a leg chord, the vertical load on the chord concentrates on the upper support face or on the lower support face of the rack piece, and the above mentioned means of positioning the engagement of the rack piece with the rack on the chord, that is, the screw spindles are often subjected to an overload. This load is liable to damage the screw spindles and also much effort is required to properly position the guide block for meshing the teeth of the rack piece with the rack.